A metal-rubber bonding system has both the high strength from the metal and the high elasticity from the rubber, and thus is used widely in various fields such as construction, ships, automobiles, aeroengines, oil-seals, conveyer belts, electrical wires, vibration absorbers and the like. At present, the metal-rubber bonding system is usually produced by the vulcanization bonding method. In particular, a metal is firstly surface-treated and then is coated in order with a primer and an adhesive, subsequently a compounded rubber sheet is placed face-to-face on the metal and then vulcanized under heating and pressing to achieve the bonding of the rubber and the metal. For example, for the vulcanization of a pulley lagging, the temperature may be 140-160° C. and the pressure may be 6-10 kg/cm2. The primers used in the vulcanization processes have been commercialized, in which the products (Chemlok®) from LORD Corporation are are the most extensively used.
The metal-rubber bonding system (for example, a pulley lagging) is typically useful for the pulleys in belt conveyers. However, when a belt conveyer is operated in a pit, the pulley lagging is often corroded by smuts and coal slimes, and the rubber layer on the pulley starts to wear away or break up due to suffering from continuously scraping of the conveyer belt buckles. Thus, the service time of the pulley is shortened as the pulley needs to be repaired. Further, the complexity of the vulcanization process makes it impossible to repair the pulley on-site. As a result, the pulleys with seriously-damaged rubber layers have to be sent to special plants for the vulcanization and rubber lagging again, which adversely affects the normal production. In addition, for a driving pulley, in order to protect the bearings during the vulcanization process and meet the clamping requirements on the pulley surface, it is necessary to disassemble undamaged couplings, bearing blocks and bearings on both ends from the driving pulley.
However, as for a driving pulley in an extra-heavy-duty belt conveyer, it is difficult in both installing by interference fit and disassembling of the couplings and bearings because of their large sizes. Moreover, the couplings and bearings are very likely to be damaged during disassembling.
Thus, there is an urgent need of an on-site process for replacing and repairing pulley laggings to shorten operation periods and cut costs. It is also desirable for such process to be carried out at a normal temperature and a normal pressure. However, the existing adhesives do not meet such requirements due to the relatively low adhesive strength at a normal temperature. For example, LDJ-245 Adhesive for rubber lagging produced by Yichang Huangshide Bond Development Co., Ltd. has a 180 degree peel strength of only 2.2 N/mm (determined according to GB/T2791-1995 and the metal material is carbon steel); and LDJ-248, a novel metal-rubber adhesive also produced by Yichang Huangshide (used together with a metal surface treating agent) has a 180 degree peel strength of 4.8 N/mm. For another example, TS853 rubber-metal adhesive which is commercially available from TONSAN Adhesive Inc., used together with 1753 primer, has a 180 degree peel strength of only 3.5 N/mm.
Consequently, there exists an urgent need of a primer for metal surfaces which can be used for bonding metal and rubber under a normal temperature and a normal pressure, and exhibits high peel strength. Such primer can meet the requirements of on-site rubber lagging on pulleys of belt conveyers.